First try at night sky photography

[lrt75914]

Hey guys,

we finally had some nice weather coming our way yesterday evening and I thought that I should have a go at night sky photography.

My main goal was to see how well my dads Skywatcher StarAdventurer could track the night sky and how his Sony Alpha 77 ii/ SAL1650 Standard Zoom Lens (16-60mm, F2.8) would handle the low light conditions. I only had enough time to take a 2" (close to Polaris) and 5" (close to the meridian) exposure and I was plagued by severe light pollution. I know the images are grainy, I know they show some severe vignetting but I do hope that they contain enough information for you to give me a feedback on how I fared on my first venture into wide-field astrophotopgraphy.

PS: I'm slightly drunk right now so this post might not make much sense. If that's the case I will try to draft a better written first (second) post, tomorrow. CHEERS

[Dave In Vermont]

It's looking good from my perch over here. I did a little looking about to see what other folks have to say about your camera. Here's one take:

https://community.sony.co.uk/t5/alpha-nex-interchangeable-lens-cameras/sony-alpha-slt-for-astrophotography/m-p/268022#M2425

And here's a Google-scope on it's working in astrophotography:

https://www.google.com/search?q=Sony+Alpha+77+ii+astrophotography&ie=utf-8&oe=utf-8

All and all, seems you have a fine camera that will serve you very well indeed. So I am looking foreward to your continued works!

Cheers!

Dave

[lrt75914]

Ok guys,

Since the first picture is unbearably noisy I decided to redo the image and make it a little bit more 'readable'.

Here are a couple of questions that I would have regarding my first attemps at noisy pictures.

1) Are the odd Shape patterns in Zoom-window 1&2 due to the Coma of the Sony lens? Is there a way to minimize or eliminate this effect?

2) The stars in the center of each image seem to be fairly round. That would lead me to believe that the StarAdventurer was properly polar aligned. I do have the feeling, however, that the stars are not really sharp. I tried to use a bahtinov mask and the edge detection program of the Sony alpha 77 ii to set the focus point but, as the pictures would suggest, failed. Is there a special trick that one can use to achieve perfect focus?

[wxsatuser]

The odd shaped stars are sagittal coma flare, commonly called the "flying bird".

It's a combination of sagittal astigmatism with coma.

Stopping down may reduce it but you have it at f/4, it may never totally disappear.

[Pompey Monkey]

Unfortunately, 2 seconds at 50 mm focal length is not a long enough exposure to determine if your polar alignment/tracking is good.

There is the so called "400" rule for star trails (there are different numbers used sometimes, but they are all in the same ballpark). Simply divide 400 by the focal length of the lens to give you the longest exposure before stars start to trail in a fixed camera image.

So in your case, you would need a minimum 8 second exposure to get trails from a fixed camera. As you are trying to track, you need to go significantly longer to see if you have any error in your PA/tracking.

[lrt75914]

Beeing the idiot I am I kind of used the wrong symbol to denote a minute. So that is a 2 minute exposure of the region around perseus and a 5 minute exposure close to the celestial equator (not the meridian).

Unfortunately, 2 seconds at 50 mm focal length is not a long enough exposure to determine if your polar alignment/tracking is good.

There is the so called "400" rule for star trails (there are different numbers used sometimes, but they are all in the same ballpark). Simply divide 400 by the focal length of the lens to give you the longest exposure before stars start to trail in a fixed camera image.

So in your case, you would need a minimum 8 second exposure to get trails from a fixed camera. As you are trying to track, you need to go significantly longer to see if you have any error in your PA/tracking.

[Eri]

as you say it looks to me like it is just out of focus, but only just a trick someone on here gave me (can't remember if it was happy-kat or Alexx or someone totally different) was to aim at a bright star like Capella and focus your camera on that using live view if you have it, when it's sharp on that star you're focused on anything else as well.

[beamer3.6m]

Great first shots.

Nail the focus and maybe buy a light pollution filter and you will be good to go.

[Alien 13]

There are a couple of things you can try, focussing on a star approx one third the distance fron the center of the frame might help with the distortion on the outer stars and I find that with camera lenses that using just liveview x10 on the very faintest star so that the focussing  effectivelly becomes an on/off action will often achieve better results.

Alan

[D4N]

Don't focus centre field either, you may have different focus across the lens so try and get a good focus somewhere between the centre and the corner of the image.

A camera lens can be a pain to focus, Baader make a handy mechanism that fits around it to help with fine focus.

/Dan

Sent from my iPad using Tapatalk

[Thalestris24]

Hi

Good polar alignment is key to getting good results with the SA. Combine that with accurate focus and you should be good to go! You need to take lots of subs (rejecting any duff ones) and stack them to improve signal/noise. I would limit exposure times to around 2 mins as the SA's periodic error in RA is quite large. A lp filter is useful but you can process out lp. Not sure how you are controlling exposures but if it's not via a laptop or tablet then an intervalometer does the job (lots on Amazon). If you have an Android tablet then there is a version of Stellarium you can get which will help you find targets.

All the best

Louise

[cjdawson]

For the focussing part, take your time.  People on here often report that it can take 30 mins to focus properly.

The Batinov mask will help, so glad you have one.

Take more images and stack them.  It will do wonders for reducing the amount of noise in the images.

Finally,  KEEP EVERY IMAGE YOU EVER TAKE... EVER!    in years to come you might find that you can reprocess old images and get more out than you thought that you could.  It might also show changes over time that you'll never be able to capture.  You might have a discovery, and not know it until you take more images of the same piece of sky.

[happy-kat]

Should also do the 1/3 ds focusing, focus on a star a third in from the edges where the 1/3 ds intersect.

Also don't use the lens wife open stop it down how far you will have to test.

Take flats.

[lrt75914]

Hey guys,

Thank you very much for all your help and the tips you gave me. I gave it another shot and came up with this image:

Equipment used:

Camera: Sony Alpha 77 ii

Lens: Sigma 105 mm F2,8 EX

Refreshment: Steaming hot safran tee

Image Inf:

Light Frames:  25x2', ISO 400, F3.5

Dark Frames: 30

Bias Frames: 30

Flat Frames: 60

To be honest, the image could be better. There is not much detail to go around and I feel like the polar alignment was a little off. Furthermore, I had a lot of trouble with dew building up on my

camera lens. It may not be a great but it's at least something .

Should also do the 1/3 ds focusing, focus on a star a third in from the edges where the 1/3 ds intersect.
Also don't use the lens wife open stop it down how far you will have to test.
Take flats.

[wxsatuser]

Think you may have more in that image that needs bringing out.

[D4N]

Nicely done, M42, M78, NGC1975 and NGC2024 all clearly visible there.

The PA seems quite good, there are some slightly eggy stars bottom left so I would guess this is e beginning of trails combined with some CA as it isn't obvious anywhere else in the image. I would just crop that bit and be happy with it

/Dan

Sent from my iPad using Tapatalk

[wxsatuser]

The Sigma 105mm will have slightly eggy stars around the edges even at f/4.5.

It's unavoidable and not to bad on widefield  unless pixel peeping.

[lrt75914]

Thank you for your feedback guys . I'll try and see if I can pull out a little bit more detail out of the picture. Right now I'll have to go to bed and get some sleep, though . 

[Alien 13]

Thats a great image.

Alan

[happy-kat]

My camera lens I use a modified black flower pot as a dew shield which I have also now flocked. Cheap and works well enough.

[lrt75914]

Hey guys,

we had a clear sky last night so I took a couple of 2 min exposures of Cassiopeia with my dad's 16-50mm/F2.8 standard zoom lens (sony sal 1650). I reduced the aperture to F4.0, set the lense to 50mm focal length and the camera to ISO800. Focusing this lens was nearly impossible. The sweet spot was nowhere to be found (utilizing the tips you gave me unfortunately didn't help much) and with the moon on the rise I used the best focus setting I could find.

Image Inf:

Light Frames:  31x2', ISO 800, F4.0

Dark Frames: 31

Bias Frames: 30

Flat Frames: 60

The obvious problem I see is that the Master Flat Frame didn't do it's job properly, balancing only the center and leaving a nasty 'ring' around the edge of the frame. Does anyone have an idea what I did wrong, here?

My Procedure for the Calibration frames:

I used a Neumann jr. Aurora Flat Field Panel to generate 2 sets of flat field frames with the panel rotated 180° between each set to cancel out any imperfections of the Aurora panel. The camera was set to AV mode as recommended by the deep sky stacker manual. The dark frames were done with the lens cap on and the settings that were used for the light frames (temperature was the same). For the bias frames I covered the viewfinder and the exposure time was reduced to 1/8000 sec. The light frames were stacked using the Kappa-Sigma Clipping mode. The Median Calibration Frames were processed using the Kappa-Sigma Frames.

[lrt75914]

After being thoroughly disappointed with the performance of my dad's standard zoom lens I thought I should give the sigma macro lens another try. I reduced the aperture to F3.5 and set the camera to ISO800. Focusing was a breeze this time around and I was able to take 45 2min subs of ngc281. Although the subs came out rather nice, stacking them resulted in the similarly disappointing image as before.

Image Inf:

Light Frames:  45x2', ISO 800, F3.5

Dark Frames: 30

Bias Frames: 30

Flat Frames: 60

Since I've been using the beta Version (3.3.4) of Deep Sky Stacker to directly process my Raw images(.ARW), I though I should convert my files to the .TIFF format and give the 'stable' Version (3.3.2) a try. This is what I came up with:

Image Inf:

Light Frames:  30x2', ISO 800, F3.5

Dark Frames: 30

Bias Frames: 30

Flat Frames: 60

What do you guys think?

[wxsatuser]

The first one looks more stretched than the second.

I have used both DSS versions and don't really see any difference.

What you have in 2minute subs looks ok to me, just the post processing needs

looking at.

Did you stretch these in DSS or some other software?

I nearly always use the 32bit Autosave tif that DSS generates for each stack.

The Autosave tif will be very dark as a rule and need stretching with software like

Pixinsight or Photoshop.

[lrt75914]

The first one looks more stretched than the second.

I have used both DSS versions and don't really see any difference.

What you have in 2minute subs looks ok to me, just the post processing needs

looking at.

Did you stretch these in DSS or some other software?

I nearly always use the 32bit Autosave tif that DSS generates for each stack.

The Autosave tif will be very dark as a rule and need stretching with software like

Pixinsight or Photoshop.

The one big problem I have with the first picture that I posted is that the stars look very flaky and out of focus. Furthermore the picture

suffers from chromatic vignetting and general color misalignment.

I tried every stacking permutation that I could find but using DSS 3.3.4 in conjunction with my .ARW files would yield similar results every single time. Since my subs look like this,

I figured either the software version or my file format was causing this problem. The final result, using DSS 3.3.2, looks like this:

The one thing that's pretty apparent is that the the stars exhibits some chromatic aberration. Unfortunately, as of this moment, I have neither PixInsight nor Photoshop at my disposable. I used Astra Image to stretch the histogram but that's about all I did since my old Macbook Pro 13" is to weak to do anything else. I did, however, order the trial license for PixInsight but until I get my new computer there is not much post processing I can do.

[wxsatuser]

DSS does'nt always align the channels spot on, it really needs sorting out in better post software.

As to focus.

One side of focus tends to give a bluish green halo around the stars and the otherside gives a redish halo.

Somewhere inbetween there is a whitish yellow which is what you look for.

If seeing is poor sometimes the red is particularly hard to get rid of, red can be seen flashing around the white

in Liveview.